Vital signs provide rapid assessment of physiological status. A normal resting heart rate for adults is 60–100 beats per minute, with well-trained athletes often having resting rates as low as 40–60 bpm; consistently elevated rates (tachycardia) or low rates (bradycardia) may indicate underlying disease. Normal blood pressure is below 120/80 mmHg, with the systolic (top) number reflecting pressure during heart contraction and diastolic (bottom) number reflecting pressure between beats; stages include elevated (120–129/<80), Stage 1 hypertension (130–139/80–89), and Stage 2 (≥140/≥90). Normal respiratory rate is 12–20 breaths per minute, and normal blood oxygen saturation (SpO2) measured by pulse oximeter is 95–100%, with values below 90% considered hypoxemia.
Common laboratory tests establish baseline health and detect disease. A complete blood count (CBC) measures red blood cells, white blood cells with differential, hemoglobin, hematocrit, and platelets, screening for infection, anemia, bleeding disorders, and blood cancers. The WBC differential distinguishes neutrophils (elevated in bacterial infections), lymphocytes (viral infections), eosinophils (allergies and parasites), monocytes, and basophils. A basic metabolic panel and comprehensive metabolic panel measure glucose, electrolytes (sodium, potassium, chloride, CO2), kidney function (BUN, creatinine), and liver function (ALT, AST, ALP, bilirubin, albumin). A lipid panel evaluates cardiovascular risk, with desirable total cholesterol below 200 mg/dL, LDL below 100 mg/dL (optimal), HDL at 60 mg/dL or higher (protective), and triglycerides below 150 mg/dL. Coagulation studies include PT/INR (extrinsic pathway, used to monitor warfarin) and PTT (intrinsic pathway, used to monitor heparin). Fasting blood sugar of 70–100 mg/dL is normal, with prediabetes at 100–125 and diabetes at 126 or higher on two occasions. The HbA1c test measures average glucose over 2–3 months. C-reactive protein (CRP) is a non-specific marker of inflammation, with high-sensitivity CRP (hs-CRP) used to assess cardiovascular risk. BNP (or NT-proBNP) is elevated in heart failure. Body Mass Index (BMI), calculated as weight in kilograms divided by height in meters squared, classifies underweight (<18.5), normal (18.5–24.9), overweight (25–29.9), and obese (≥30).
Medical imaging provides visualization of internal structures. X-rays are fast and inexpensive, ideal for bones and chest evaluation. Computed tomography (CT) combines multiple X-rays for cross-sectional images and excels in emergencies for detecting bleeding and fractures. Magnetic resonance imaging (MRI) uses magnetic fields and radio waves to produce detailed images of soft tissues (brain, spinal cord, joints) without radiation. Ultrasound uses sound waves for real-time imaging, with no radiation exposure, making it the standard for pregnancy monitoring and many bedside applications. Positron emission tomography (PET) detects metabolically active areas and is widely used in cancer staging. Other specialized tests include arterial blood gas (ABG) analysis for oxygenation and acid-base balance, electrocardiogram (ECG/EKG) for heart rhythm, echocardiogram for cardiac structure and function, spirometry for pulmonary function, colonoscopy for colorectal cancer screening (recommended from age 45), DEXA scan for bone density, and lumbar puncture for cerebrospinal fluid analysis. A screening test detects potential disease in asymptomatic people and prioritizes sensitivity, while a diagnostic test confirms or rules out disease with greater specificity.